99 M3. Fully auto top. Brand new top/brand new tension straps/brand new tonneau cover struts. Top worked perfectly fine, but recently got stuck halfway position during lowering of the top. Did the re-synch process (pull the lever under back seat, then manually stow the top, close the tonneau cover lid, open trunk, re-engage motors, get in car, press and hold convertible top button, wait a few seconds, and top closes properly. Start the car, press button to lower the top, lowers fine this time. Press button to close, top closes fine.
But..what is causing the top to get stuck halfway open randomly? Everything appears to fold properly, there is no colliding of any parts during the opening/closing process.
Are you sure you got the right tension on the straps? Mine occasionally hangs up like that and I suspect it's strap tension failing to lift the back bow in order to clear the tonneau cover.
If you do not hear any interference (motors clanking, tonneau hitting the top etc) then it may be microswitch, length of the operation rods or the module itself. Can you post a video to show exactly where it stops?
Or
1) does it fully unlock at the windshield and then the rear bow does not come up,
2) rear bow is fully up and tonneau does not open
3) tonneau opens and bow does not drop
4) bow drops but remainder of top does not start to retract
5) tonneau will not close
or somewhere in the middle of all that......
There is a pdf file in one of the sticky posts for this forum that describes the roof operation logic, and based on that it is possible to determine what the problem with the roof is. Unfortunately the pdf doesn't offer any solutions if specific parts of the process fails, so here are some suggestions based on the problems in the scenarios identified in the post above:
1 - I'll ignore this because you say the roof is 'halfway' open
2 - If the rear bow is up and the tonneau doesnt open, this is most likely the microswitch at the bottom left side of the the roof frame is not being (dis)engaged* or faulty.
The roof push-rod interacts with this microswitch, and it may be that the pushrod may require a slight adjustment.
*It has been a while since I looked at the pdf or the state of the switch on my car so I cant remember if it should be engaged or disengaged at this step of the process.
3 - Tonneau opens and bow does not drop.
This could be due to the sensor on the cover motor not being engaged which signals that the cover is in the correct position, and that the roof frame motor should begin. The sensor IS adjustable, but every document I have read advise NOT adjusting this.
I dont have a suggestion for how to fix this.
4 - bow drops but the remainder of the roo fails to retract
If the roof sticks halfway during lowering (after the rear bow is lowered into the storage compartment), it is usually a result of the front bow not being backwards - when this happens, the rear bow applies full tension and locks into place.
When it sticks in this position, instead of giving up, press the up button (to release some tension) and manually pivot the front bow backwards, and then continue to lower the roof.
You mention that the tension straps are new.... at the front as well as the elastic part there is another section which is designed to bend and it may be that this part is not bending as intended - mine used to have this problem (in fact it still doesnt bend as designed), but I manually assist it so that the front of the roof folds and stores correctly. I have had my hardtop on for most of the year so I havent gotten around to fixing this issue yet.
The folding of the front section of the roof enables the headliner to fold properly and store correctly. There IS a more permanent fix to this posted in this forum somewhere - I think Palamino posted it - described as a "Headliner Fix".
5 - Tonneau will not close
The same sensor as in point 2 needs to be (dis)engaged * to signal the cover motor to begin again. Considering that the roof has gotten this far in the operation process, the pushrod could require a slight adjustment.
*It has been a while since I looked at the pdf or the state of the switch on my car so I cant remember if it should be engaged or disengaged at this step of the process.
When troubleshooting, be aware that it IS ok to stop the roof opening process by letting go of the switch - that will not cause the roof system to become unsynchronised (is that an actual word?). Even changing direction of roof operation mid-process will not cause the roof to forget its settings. This should allow you to examine the positions of pushrods and status of frame sensors which could help determine the cause of your problem.
Feel free to post up any follow-up questions.
Good luck
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